Field of the Invention
The invention relates to a heat exchanger for an air conditioner, and more particularly to a cooling fin for a heat exchanger which provides an improved heat transfer performance.
A conventional heat exchanger for an air conditioner includes, as shown in FIG. 1, a plurality of flat vertical fins 1 arranged in a parallel relation to each other at predetermined intervals and a plurality of heat exchanging tubes 2 passing horizontally through the fins 1 perpendicular thereto. The air currents flow in the spaces defined between the fins 1 in the direction of the arrow in FIG. 1 and exchange heat with the fluid flowing in the heat exchanging tubes 2.
For a thermal fluid flowing around each flat fin 1, there has been known that the thickness of the thermal boundary layer 3 on both heat transfer surfaces of the fin 1 is gradually thickened in proportion to square root of the distance from the air current inlet end of the fin 1 as shown in FIG. 2. In this regard, the heat transfer rate of the fin 1 is remarkably reduced in proportion to the distance from the air current inlet end. Therefore, the above heat exchanger has a lower heat transfer efficiency.
For the thermal fluid flowing about each heat transfer pipe 102, it has been also known that, when lower velocity air currents flow in the direction of the arrow of FIG. 3, the air currents separate from the outer surface of the pipe 2 at portions spaced apart from the center point of outer surface of the pipe 4 at angles of 70-degree to 80-degree. Therefore, an air dead region 4 is formed behind each tube 2 in a direction of the air flow as shown in the hatched region of FIG. 3. In the air dead region 4, the heat transfer rate of the tube 2 is remarkably reduced so that the heat transfer efficiency of the above heat exchanger becomes worse.
In order to overcome the above problems, there has been proposed another solution as disclosed in Korean Patent Application No. 96-27642 filed on Jul. 9, 1996 by the present applicant. This heat exchanger, as shown in FIGS. 4 and 5, includes a plurality of heat exchanging tubes 2 which are fitted into the regularly spaced flat fins 1 such that the tubes 2 are perpendicular to the fins 1. The heat exchanger also includes a plurality of angled louver patterns which are formed adjacent the tubes 2 passing through each fin 1. Each louver pattern comprises a pair of louver groups located either above or below one of the tubes 2. A lower louver pattern disposed below a tube 2 comprises a first louver group 20 configured to guide an air current flow in a first direction, and a second louver group 40 which is inclined opposite to the first louver group such that the guided air current is guided in a different direction. An upper louver pattern located above a tube 2 comprises a third louver group 30 and a fourth louver group 50 inclined relative to one another. Each of the louver groups is radially oriented relative to a respective tube 2.
The first and third louver groups 20 and 30 are oriented in mirror image relationship to each other such that the air currents flowing over both surfaces of the flat fin 1 and in the area between adjacent tubes 2 become turbulent and mixed. Further, the second and fourth louver groups 40 and 50 are similarly placed in mirror image relationship to each other such that the air currents which have passed the groups 20 and 30 continue to traverse the remainder of the area between the tubes 2 and become turbulently mixed by the groups 40 and 50, thereby reducing the dead air region.
Each of the louver groups includes louvers 70-75 which are inclined obliquely relative to the plane of the fin, as can be seen in FIG. 5. That is, each of the louvers 71-74 has a left end L projecting past a first surface S1 of the flat fin 1, and a right end R thereof extending past a second surface S2 of the flat fin 1. Each louver provides a slit arranged transversely relative to the air flow. The louvers are formed by way of a cutting and twisting process so as to be integral with the flat fin 1. The fin 1 includes flat, solid portions 60, some of which are round and surround respective tubes 2. For example, one of those round areas occupies a region between upper ends of the louver groups 20, 40 and a lower outer circumference of an adjacent tube 2. The louver groups are radially oriented with respect to respective tubes 2.
The first and second louver groups 20, 40 are arranged symmetrical relative to each other and are separated by a solid portion 60 of the fin. The same is true of the third and fourth groups 30 and 50.
The louvers 70-75 of each group are sequentially arranged relative to one another without any solid fin portion disposed therebetween.
In the drawing, reference numeral 80 denotes beads or ridges which are vertically oriented. Each bead 80 defines a vertical longitudinal axis that perpendicularly intersects the axes of vertically adjacent pipes 2. The beads serve as water guides to drain water, or dew, that condenses on the tubes 2 or fins. The beads also reinforce the fin 1 and enlarge the surface area thereof.
Each bead 80 is located in a solid portion 60 of the fin situated between the first and third groups 20, 30 on the one hand, and the second and fourth groups 40, 50 on the other hand.
The bead projects above the plane of the fin 1 and has a V-shaped cross-section (see FIG. 5).
In the heat exchanger described above, each louver group has a remote edge e facing away from a respective lower group and facing an edge of another louver group and extending parallel with respect to a direction s of the air flow. The air current flowing over those edges e is not well mixed, resulting in the creation of a wider dead air region behind each tube 2, as well as an increase in the pressure drop, thereby reducing the heat transfer efficiency of the heat exchanger.
Furthermore, since the beads are formed only in vertical alignment with the tubes 2, the strength of portions of the fin 1 disposed in front of and behind the tubes 2 is not improved, which greatly lowers the overall strength of the fin 1. In addition, there are insufficient beads to satisfactorily drain all of the dew formed on the surface of the fin 1.